Core binder



nited States Patent 2,974,050 CORE BINDER Thomas E. Barlow,McHenry,'lll., assignor to International Minerals & ChemicalCorporation, a corporation of New York t No Drawing. Filed June 27,1958, Ser. No. 744,917

5 Claims. (Cl. 106-385) The present inventionrelates to foundry cores.More particularly, it relates to an improved foundry core of high hotstrength, containing a binder having superior properties. 1 1

In foundry practice, it is frequently necessary to incorporate cores inthe molds to produce'void spaces in the metal castings. Such cores areordinarily prepared by compacting sand in the desired shape. In orderfor thecore to have sufiicient mechanical strength to withstand theimpact of the hot metal, it is customary to incorporate one or moresubstances in the coremixture and thereafter to bake the core atelevated temperature before assembling it into the mold. A wide range ofsubstances have been employed for this purpose, including cerealproducts, water glass, drying oils, resins, sulfite liquor,

proteinaoeous materials,-molasses, clays, wood fiour, gelatinizedstarches, dextrinized starches, and the like. The present inventioninvolves a novel combination of substances for use as a core binder,whereby cores of superior strength at casting temperaures are obtained.

One object of the present invention is to prepare starch or starchfraction comprising gelatinized amylo' pectin, and a phosphate salt ofvan alkali metal or an alkaline -earthamet-al. The resulting mixture isformed into the desired shape. and is thereafter baked underconventional conditions. The core obtained thereby has excellent bakedtensile strength and outstanding hot properties.

' In preparing a foundry core according to ,one embodimer t of thepresent invention, sand is mulled with between about 3 and about 6% byWeight ofi'water, optimallyaround 4 to 5%. added in a proportion betweenabout-0.5 and about 2.5% by weight of the sand, dry basis, and ismulledin. Finally, the phosphate salt is added in a proportion betweenaboutS and about 25% by-weight offthe. amylopectin,

lg drybasis, and the entiretmixture is mulled until homogenews. Themulling steps ordinarily require-periods of' about 1, 1, and 6 minutes,respectively, for completion. Other materials of the typescommonlyemployed as core binders may also be incorporated the coremixture if desired.

Gelatinizedamylopectin is then v The cores produced in accordance withthe present invention are baked under conventional conditions.' Therequired temperature and'tirne will vary considerably, as theprior artrecognizes, according to the size of the core,

the surface-to-volume ratio, the water content, and the Laboratoryreasinglylonger baking times, particularly cores'iwhich 1,

:of thebaked cores was measured interms cfitlieirteiisile strengthatroom temperature. (baked strength) and in have lower surfacerto-volumeratios. Higher tempera.- tures may'in many cases be employed, but aregenerally not preferred, owing to a tendency of the cores to become Ioverbaked and case-hardened. V I

Other procedures may be employed satisfactorily in the preparation ofthe core mixture. For example, the sand the gelatinized amylopectin, thephosphate'salt, and any other dry ingredients can first be mulledtogether, followed by the water and any other wet ingerdients. Inanother method, the phosphate salt can be dissolved in the water, thenmulled with the sand, followed by the gelatinizcd amylopectin. Themethod and sequence of admixing the various components can be varied atwill while still producing-improved results in the resulting cores; Themulling times employed are not critical, so long as a homogeneousmixturelof the materials is achieved. For this purpose, it is ordinarilysufficient to mull the initial admixtures, if any, for only about 1minute, and to mullthmcompleted, mixture for about 5 to -l()minutes,ppreferably around 6 minutes.

Starch generally comprises two primary fractions- -viz., amylopectin andamylase, the proportions varying, markedly. from one starch to another.The present invention can suitably employ either amylopectin, or wholestarch, or a starch fraction comprising arnylopectin, so long as thesaid-materials have been subjected to gel,- atinization. In this respectit should be noted that amylo pectin, as ordinarily marketed, is ingelatinized form owing to the method by which it is separated from .theoriginal starch. It should further be noted that the so.- called'foundrycereals are invariably gelatinized starch of one type or. another,always comprising arnylopectin', land aresatisfactory for use in thepresent invention." 'Suitable salts forusetin the present invention arethe Water-soluble orthophosphate, pyrophosphate,.1metaphos, phate, andpolyphosphateisalts of the alkali metals and of the alkaline-earth ess,or mixtures thereof, which have a composition yielding a; saturatedaqueous solution of a pHbetween about4' and-about 7 at 25 C. such salts:or saltinixtures can conveniently be prepared byi reacting a phosphoricacidw-ith a basic alkali metal'or' alkaline earthmetal-compound inaqueous solution while adjusting'the proportions to reach thedesiredpI-Ilevel. A preferred type of salt is 'a mixture of monosodiurii'or'th'ophosphate and disodium orthoprosphate having a 'pH of about 6.Another preferred salt is sodium metaphosphate. Other suitable saltsinclude mixtures-of monopotassium and dipotassiurn orthophosph atesjmixtures of monocalciurn dicalcium ortho-phosphates, and the like,within the broad definitionsetl forth above. The following specificexamples will more clearlyillustrate the invention. All of the testsdescribedtherein were carried out according" to stand'ard methodsdefined ill: the Foundry Sand Handbook, '6tl'i' edition #1952) publishedby the American Foundrymens Societyj'fChicago. Except as noted below,all of the testsieinployed fineness of 62 '(.AGI 62). Measurements werebased upon tthet'dry weight of, sand-..empl yfiirtbil ll ll sllh carriedout in a laboratory-size Simpson muller.. After mulling was completedtlie coreimixture was discharged from the muller and stored'in 'a'sealedcan-until used tb make cores? "The cores werebaked'ar 425 "F'."for' 15minutes, then cooled toj roomltemperature. The strength terms of thetime jrequiredfor them to collapse'at 800 the reported results arethelaverag e J Gelstlntzed corn starch Example 1 The following exampleillustrates the effectiveness of gelatinized amylopectin in combinationwith mixed sodium orthophosphates as a core binder. The phosphate saltmixture was a blend of disodium orthophosphate dihydrate and monosodiumorthophosphate monohydrate in 2.54:1 ratio by weight. The compositionand preparation of the core mixtures were as follows:

% water 0.15% phosphate salts 0.85% gelatinized amylopectin Remaindersand The sand and water were mulled 1 minute; the phosphate salt mixturewas added and mulled for 1 minute; and the gelatinized amylopectin wasadded and mulling was continued for 6 minutes. The completed mixtureretained 5.1% water. Cores prepared therefrom had a baked strength of200 p.s.i. and a breakdown time of 11.33 minutes.

For comparison, a core mixture was prepared in a similar manner,omitting the phosphate salts. The resulting cores had a high bakedstrength, 290 p.s.i., but the breakdown time was only 3.07 minutes.

For further comparison, two core mixtures were prepared with 0.25 and0.5% of phosphate salts, omitting the gelatinized amylopectin. Coresprepared therefrom had baked strengths of only and p.s.i., respectively,and were not tested for breakdown time.

Example 2 Mixed sodium orthophosphates were dissolved in water andmulled with sand for 1 minute. Gelatinized amylopectin was then added,and mulling was continued for 6 minutes. The materials, proportions, andprocedure were otherwise the same as described in Example 1. The coresprepared therefrom had a baked strength of 225 p.s.i. and a breakdowntime of 9.90 minutes.

Example 3 The following example illustrates the use of gelatinized wholecorn starch in combination with phosphate salts as a core binder. Thestarch was prepared by wetting it with water and passing it downwardbetween rotating drums heated with steam under pressure. By this means,the starch was simultaneously gelatinized and dried in the form of athin film. Before use, the starch was ground to a fine state ofsubdivision. Cores were prepared according to the procedure of Example1, substituting the gelatinized corn starch for gelatinized amylopectin.The resulting cores had a baked strength of 190 p.s.i. and a breakdowntime of 9.57 minutes.

For comparison, three additional groups of cores were prepared in ananalogous manner using ungelatinized whole corn starch alone as the corebinder, ungelatinized whole corn starch plus the sodium orthophosphatesalt mixture referred to above, and gelatinized whole corn starch alone.Cores prepared therefrom were far inferior in breakdown time:

Breakdown Time, min.

Baked Ungelattnized corn starch Same, plus phosphates Example 4 A coremixture was prepared according to the. procedure described in Example 1,using 0.25% of the sodium orthophosphate salt mixture and 0.1% of astandard foundry cereal (i.e., a gelatinized starch preparation). Coresprepared therefrom had a baked strength of 165 p.s.i. and breakdowntimes of 7.37 minutes at 800- F. and 5.82 minutes at 1000" F.

For comparison, a core mixture was prepared according to the procedureof Example 1, employing only a foundry cereal at the 1.0%. level as thecore binder. Cores prepared therefrom had a baked strength of onlyp.s.i. and a breakdown time of only 1.45 minutes at 100 F.

Example 5 A core mixture was prepared as in Example 1, replacing thesodium orthophosphate mixture with 0.2% of sodium metaphosphate. Coresprepared therefrom had a baked strength of p.s.i. and a breakdown timeof 10.64 minutes at 800 F.

The foregoing description refers to numerous details of core mixturecomposition, preparation techniques, and the like, for the purpose ofillustrating and clarifying the invention, but in no respect by way oflimitation. It will be apparent that numerous modifications andequivalents of the invention will be suggested thereby to those skilledin the art.

The following claims particularly point out and distinctly claim thesubject matter of the invention:

I claim:

1. In a method for producing a foundry core, which method comprisescommingling sand, water, and binder, forming the resulting mixture intothe desired shape, and baking the shaped mixture at a temperaturebetween about 350 and about 450 F., the improvement which comprisesemploying as said binder, in combination, at least about 0.5% by weightof gelatinized amylopectin, based on the 'dry weight of sand containedin the core mixture, and a phosphate salt selected from the groupconsisting of the water-soluble alkali-metal and alkaline-earthmetalphosphates and mixtures thereof which produce a pH between about 4 and 7in saturated aqueous solution at about 25 C., the proportion of saidphosphate salt :being between about 5 and about 25% by weight, basedupon said gelatinized amylopectin.

2. The method of claim 1 wherein said gelatinized amylopectin isemployed in a proportion between about 0.5 and about 2.5% by weight,based upon the dry weight of sand contained in the core mixture.

3. The method of claim 1 wherein said phosphate salt is an alkali-metalorthophosphate.

4. The method of claim 1 wherein said phosphate salt is a metaphosphate.

5. In the method for producing a foundry core, which method comprisescommingling sand, water, and binder, forming the resulting mixture intothe desired shape, and baking the shaped mixture at a temperaturebetween about 350 and about 450 F., the improvement which comprisesemploying as said binder, in combination, gelatinized Whole starchcontaining between about 0.5 and about 2.5% by weight of gelatinizedamylopectin, based upon the dry weight of sand contained in the coremixture, and a sodium orthophosphate of a composition which produces apH between about 4 and about 7 in saturated aqueous solution at about 25C., the proportion of said sodium orthophosphate being between about 5and about 25% by weight based upon said gelatinized amylopectin.

References Cited in the file of this patent UNITED STATES PATENTS1,531,871 Nagel Mar. 31, 1925 1,974,915 Giesecke Sept. 25, 19342,779,693 Pacsu et al Jan. 29, 1957 2,884,412 Neukom Apr. 28, 1959FOREIGN PATENTS 515,470 Great Britain Dec. 6, 1939 543,202 Great BritainFeb. 13, 1942 7 770,561 Great Britain Mar. 20, 1957 879,150 Germany June11, 1953 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent.No. 2 974,o5o March '2 1961 I Thomas E. Barlow It is hereby certifiedthat error appears in the above numbered patent requiring correction andthat the said Letters Patent should read as corrected below Column 4line 6 for "100 F," read 1000 F. V column 4 line 35 for about 4 and '1"read about 4 and about 7 Signed and sealed this 29th day of August 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

1. IN A METHOD FOR PRODUCING A FOUNDRY CORE, WHICH METHOD COMPRISESCOMMINGLING SAND, WATER, AND BINDER, FORMING THE RESULTING MIXTURE INTOTHE DESIRED SHAPE, AND BAKING THE SHAPED MIXTURE AT A TEMPERATUREBETWEEN ABOUT 350 AND ABOUT 450*F., THE IMPROVEMENT WHICH COMPRISESEMPLOYING AS SAID BINDER, IN COMBINATION, AT LEAST ABOUT 0.5% BY WEIGHTOF GELATINIZED AMYLOPECTIN, BASED ON THE DRY WEIGHT OF SAND CONTAINED INTHE CORE MIXTURE, AND A PHOSPHATE SALT SELECTED FROM THE GROUPCONSISTING OF THE WATER-SOLUBLE ALKALI-METAL AND ALKALINE-EARTHMETALPHOSPHATES AND MIXTURES THEREOF WHICH PRODUCE A PH BETWEEN ABOUT 4 AND 7IN SATURATED AQUEOUS SOLUTION AT ABOUT 25*C., THE PROPORTION OF SAIDPHOSPHATE SALT BEING BETWEEN ABOUT 5 AND ABOUT 25% BY WEIGHT, BASED UPONSAID GELATINIZED AMYLOPECTIN.